Field of the Invention
The present invention relates to constant current generation circuits and microprocessors including them and in particular to a constant current generation circuit that outputs a current having a stable current value against variation of temperature and a microprocessor including it.
Description of the Related Art
In the circuits of semiconductor devices, a constant current generation circuit that generates a constant current for setting the operating current of a circuit or the operating characteristics of a circuit is frequently utilized. (The examples of the operating characteristics include the oscillating frequency of an oscillation circuit, the delay time of a delay circuit, and the like.) Constant current generation circuits may be required to maintain a constant current value regardless of the temperature of a semiconductor substrate. This is because temperature variation in the operating characteristics of a circuit due to the temperature of a semiconductor substrate can be suppressed by taking the following measure: variation in output current (temperature variation in output current) due to the temperature of the semiconductor substrate is suppressed.
A technology for suppressing variation in output current due to the temperature of a semiconductor substrate as mentioned above is described in Patent Document 1. FIG. 17 is a block diagram of the RC oscillator described in Patent Document 1. In the RC oscillator 100 illustrated in FIG. 17, a bias circuit portion 101 outputs current IRAMP based on the resistance value of a resistor R. A ramp/hold circuit portion 102 generates voltage VHOLD having a gradient in proportion to the magnitude of current IRAMP.
In the RC oscillator 100, resistors Ra, Rb are coupled in series to form the resistor R. The resistance value of the resistor Ra is reduced as the temperature rises and the resistance value of the resistor Rb is increased as the temperature rises. That is, in the RC oscillator 100, the resistor R is configured by combining two resistors having such characteristics that their resistance values oppositely fluctuate with temperature; and fluctuation in the resistance value of the resistor R with temperature is thereby suppressed. In the RC oscillator 100, temperature variation in the current value of current IRAMP generated based on the resistance value of the resistor R is thereby suppressed.
A method in which temperature variation in the resistance value of an entire resistor is suppressed by combining two resistors having opposite fluctuation characteristics with temperature is also disclosed in Patent Documents 2 and 3.
[Patent Document 1]
Japanese Patent No. 4460588
[Patent Document 2]
Japanese Patent Application Publication No. 2005-286021
[Patent Document 3]
Japanese Patent Application Publication No. 2005-333298